One year into her marriage to her husband, Kenji, Chigusa Matsuyama had been enjoying a happy life. But just before their wedding anniversary, Kenji suggested that his older brother, Kazuhiko, who was searching for a new job, stay at their home temporarily as a brother-in-law. To make matters worse, Kenji had to leave town for a business trip, leaving Chigusa alone on their special day. After seeing her husband off, Chigusa felt at ease with her friendly brother-in-law—until Kazuhiko, drawn to her vulnerable state, suddenly pinned her down. In that instant, Chigusa's heart and body were overwhelmed by unfamiliar sensations, and she could no longer resist the pleasure. Since then, the unforgettable experience replayed in her mind again and again, pulling her deeper into a whirlpool of new, uncontrollable emotions.